Sensorless Control Of Brushless DC Motor In Full Speed Range

The traditional brushless DC motor control system uses the position sensor to obtain the commutation signal and speed feedback signal for control.However,the presence of the position sensor increases the size of the motor,increases the number of leads,and reduces the reliability,which limits the use of the motor in many occasions.Therefore,the positionless control technology has become a current research hotspot.In addition,as the application environment of brushless DC motors becomes more and more complicated,the control system is often affected by external uncertain disturbances and perturbations of internal parameters.Therefore,it is necessary to study new high-performance control algorithms to improve the performance and quality of the control system.Under the requirements of the above objectives,this paper focuses on improving the performance of the positionless control system of the brushless DC motor,and discusses and studies the following aspects.First,the working principle and mathematical model of the brushless DC motor are briefly described,and the principle and speed calculation formula of the motor commutation through the line back-EMF are analyzed,in order to provide a research basis for the brushless DC motor line back-EMF sliding mode observer algorithm and sliding mode variable structure control algorithm.Secondly,combining the mathematical model of the brushless DC motor and the sliding mode control theory,a traditional sliding mode observer that can directly observe the back-EMF of the motor line is derived.Aiming at the problem of inaccurate motor commutation signals caused by excessive system chattering of the traditional sliding mode observer,an improved sliding mode observer is proposed.The observer uses a smooth continuous sigmoid function as the system switching function,and derives a sliding mode gain that can vary with the speed according to Lyapunov theorem.When the speed signal calculated by the line back-EMF observation value is used for motor speed closed-loop control,the PID regulator in the traditional speed closed-loop control is susceptible to external disturbances and motor parameter changes.Therefore,a speed sliding mode controller based on power reaching law is designed to realize the speed robust control of the motor.At the same time,the motor cannot start automatically without position control,so a three-stage starting method suitable for this control system is adopted.Finally,a system simulation model was built under MATLAB/Simulink environment for simulation analysis,and using DSP-TMS320F28335 as the control core to build a control system experiment platform for experimental verification.The simulation and experimental results show that compared with the traditional sliding mode observer,the peak error of the line back-EMF observation at 400r/min and 3000r/min is reduced by 70% and 54.8% respectively,obtains more accurate commutation signals.At the same time,compared with the speed PID control,the speed sliding mode control has a fast response,small overshoot,strong robustness to the internal parameter changes and external disturbances of the motor,and improves the performance of the brushless DC motor positionless control system.